diff --git a/.changeset/tidy-ads-greet.md b/.changeset/tidy-ads-greet.md
new file mode 100644
index 000000000..13c4e2b72
--- /dev/null
+++ b/.changeset/tidy-ads-greet.md
@@ -0,0 +1,5 @@
+---
+'@lion/collapsible': minor
+---
+
+Added types for collapsible package.
diff --git a/packages/collapsible/demo/CustomCollapsible.js b/packages/collapsible/demo/CustomCollapsible.js
index ca57ea5d1..560334606 100644
--- a/packages/collapsible/demo/CustomCollapsible.js
+++ b/packages/collapsible/demo/CustomCollapsible.js
@@ -6,10 +6,9 @@ const EVENT = {
 };
 /**
  * `CustomCollapsible` is a class for custom collapsible element (`<custom-collapsible>` web component).
- *
  * @customElement custom-collapsible
- * @extends LionCollapsible
  */
+// @ts-expect-error false positive for incompatible static get properties. Lit-element merges super properties already for you.
 export class CustomCollapsible extends LionCollapsible {
   static get properties() {
     return {
@@ -26,15 +25,13 @@ export class CustomCollapsible extends LionCollapsible {
   }
 
   connectedCallback() {
-    if (super.connectedCallback) {
-      super.connectedCallback();
-    }
-    this._contentNode.style.setProperty(
+    super.connectedCallback();
+    this._contentNode?.style.setProperty(
       'transition',
       'max-height 0.35s, padding 0.35s, opacity 0.35s',
     );
     if (this.opened) {
-      this._contentNode.style.setProperty('padding', '12px 0');
+      this._contentNode?.style.setProperty('padding', '12px 0');
     }
   }
 
@@ -51,6 +48,7 @@ export class CustomCollapsible extends LionCollapsible {
   /**
    * Trigger show animation and wait for transition to be finished.
    * @param {Object} options - element node and its options
+   * @param {HTMLElement} options.contentNode
    * @override
    */
   async _showAnimation({ contentNode }) {
@@ -66,20 +64,22 @@ export class CustomCollapsible extends LionCollapsible {
   /**
    * Trigger hide animation and wait for transition to be finished.
    * @param {Object} options - element node and its options
+   * @param {HTMLElement} options.contentNode
    * @override
    */
   async _hideAnimation({ contentNode }) {
     if (this._contentHeight === '0px') {
       return;
     }
-    ['opacity', 'padding', 'max-height'].map(prop => contentNode.style.setProperty(prop, 0));
+    ['opacity', 'padding', 'max-height'].map(prop => contentNode.style.setProperty(prop, `${0}`));
     await this._waitForTransition({ contentNode });
   }
 
   /**
    *  Wait until the transition event is finished.
    * @param {Object} options - element node and its options
-   * @returns {Promise} transition event
+   * @param {HTMLElement} options.contentNode
+   * @returns {Promise<void>} transition event
    */
   _waitForTransition({ contentNode }) {
     return new Promise(resolve => {
@@ -100,7 +100,7 @@ export class CustomCollapsible extends LionCollapsible {
 
   /**
    * Calculate total content height after collapsible opens
-   * @param {Object} contentNode content node
+   * @param {HTMLElement} contentNode content node
    * @private
    */
   async __calculateHeight(contentNode) {
diff --git a/packages/collapsible/src/LionCollapsible.js b/packages/collapsible/src/LionCollapsible.js
index 748e34a2b..237b3b2c5 100644
--- a/packages/collapsible/src/LionCollapsible.js
+++ b/packages/collapsible/src/LionCollapsible.js
@@ -44,34 +44,40 @@ export class LionCollapsible extends LitElement {
   }
 
   connectedCallback() {
-    if (super.connectedCallback) {
-      super.connectedCallback();
-    }
+    super.connectedCallback();
+
     const uid = uuid();
-    this._invokerNode.addEventListener('click', this.toggle.bind(this));
+
+    if (this._invokerNode) {
+      this._invokerNode.addEventListener('click', this.toggle.bind(this));
+      this._invokerNode.setAttribute('aria-expanded', `${this.opened}`);
+      this._invokerNode.setAttribute('id', `collapsible-invoker-${uid}`);
+      this._invokerNode.setAttribute('aria-controls', `collapsible-content-${uid}`);
+    }
+
+    if (this._contentNode) {
+      this._contentNode.setAttribute('aria-labelledby', `collapsible-invoker-${uid}`);
+      this._contentNode.setAttribute('id', `collapsible-content-${uid}`);
+    }
+
     this.__setDefaultState();
-    this._invokerNode.setAttribute('aria-expanded', this.opened);
-    this._invokerNode.setAttribute('id', `collapsible-invoker-${uid}`);
-    this._invokerNode.setAttribute('aria-controls', `collapsible-content-${uid}`);
-    this._contentNode.setAttribute('aria-labelledby', `collapsible-invoker-${uid}`);
-    this._contentNode.setAttribute('id', `collapsible-content-${uid}`);
   }
 
   /**
    * Update aria labels on state change.
-   * @param {Object} changedProps - changed props
+   * @param {import('lit-element').PropertyValues } changedProperties
    */
-  updated(changedProps) {
-    if (changedProps.has('opened')) {
+  updated(changedProperties) {
+    if (changedProperties.has('opened')) {
       this.__openedChanged();
     }
   }
 
   disconnectedCallback() {
-    if (super.disconnectedCallback) {
-      super.disconnectedCallback();
+    super.disconnectedCallback();
+    if (this._invokerNode) {
+      this._invokerNode.removeEventListener('click', this.toggle);
     }
-    this._invokerNode.removeEventListener('click', this.toggle);
   }
 
   /**
@@ -105,28 +111,34 @@ export class LionCollapsible extends LitElement {
 
   /**
    * Show animation implementation in sub-classer.
+   * @param {Object} opts
    * @protected
    */
-  // eslint-disable-next-line class-methods-use-this, no-empty-function
-  async _showAnimation() {}
+  // eslint-disable-next-line class-methods-use-this, no-empty-function, no-unused-vars
+  async _showAnimation(opts) {}
 
   /**
    * Hide animation implementation in sub-classer.
+   * @param {Object} opts
    * @protected
    */
-  // eslint-disable-next-line class-methods-use-this, no-empty-function
-  async _hideAnimation() {}
+  // eslint-disable-next-line class-methods-use-this, no-empty-function, no-unused-vars
+  async _hideAnimation(opts) {}
 
   get _invokerNode() {
-    return Array.from(this.children).find(child => child.slot === 'invoker');
+    return /** @type {HTMLElement[]} */ (Array.from(this.children)).find(
+      child => child.slot === 'invoker',
+    );
   }
 
   get _contentNode() {
-    return Array.from(this.children).find(child => child.slot === 'content');
+    return /** @type {HTMLElement[]} */ (Array.from(this.children)).find(
+      child => child.slot === 'content',
+    );
   }
 
   get _contentHeight() {
-    const size = this._contentNode.getBoundingClientRect().height;
+    const size = this._contentNode?.getBoundingClientRect().height || 0;
     return `${size}px`;
   }
 
@@ -136,7 +148,9 @@ export class LionCollapsible extends LitElement {
    */
   __openedChanged() {
     this.__updateContentSize();
-    this._invokerNode.setAttribute('aria-expanded', this.opened);
+    if (this._invokerNode) {
+      this._invokerNode.setAttribute('aria-expanded', `${this.opened}`);
+    }
     this.dispatchEvent(new CustomEvent('opened-changed'));
   }
 
@@ -145,12 +159,14 @@ export class LionCollapsible extends LitElement {
    * @private
    */
   async __updateContentSize() {
-    if (this.opened) {
-      this._contentNode.style.setProperty('display', '');
-      await this._showAnimation({ contentNode: this._contentNode });
-    } else {
-      await this._hideAnimation({ contentNode: this._contentNode });
-      this._contentNode.style.setProperty('display', 'none');
+    if (this._contentNode) {
+      if (this.opened) {
+        this._contentNode.style.setProperty('display', '');
+        await this._showAnimation({ contentNode: this._contentNode });
+      } else {
+        await this._hideAnimation({ contentNode: this._contentNode });
+        this._contentNode.style.setProperty('display', 'none');
+      }
     }
   }
 
@@ -159,7 +175,7 @@ export class LionCollapsible extends LitElement {
    * @private
    */
   __setDefaultState() {
-    if (!this.opened) {
+    if (!this.opened && this._contentNode) {
       this._contentNode.style.setProperty('display', 'none');
     }
   }
diff --git a/packages/collapsible/test/lion-collapsible.test.js b/packages/collapsible/test/lion-collapsible.test.js
index 94bd93681..a3848d266 100644
--- a/packages/collapsible/test/lion-collapsible.test.js
+++ b/packages/collapsible/test/lion-collapsible.test.js
@@ -1,7 +1,14 @@
-import { expect, fixture, html } from '@open-wc/testing';
+import { expect, fixture as _fixture, html } from '@open-wc/testing';
 
 import '../lion-collapsible.js';
 
+/**
+
+ * @typedef {import('../src/LionCollapsible').LionCollapsible} LionCollapsible
+ * @typedef {import('lit-html').TemplateResult} TemplateResult
+ */
+const fixture = /** @type {(arg: TemplateResult) => Promise<LionCollapsible>} */ (_fixture);
+
 const collapsibleTemplate = html`
   <button slot="invoker">More about cars</button>
   <div slot="content">
@@ -10,12 +17,16 @@ const collapsibleTemplate = html`
   </div>
 `;
 let isCollapsibleOpen = false;
+/** @param {boolean} state */
 const collapsibleToggle = state => {
   isCollapsibleOpen = state;
 };
 const defaultCollapsible = html` <lion-collapsible>${collapsibleTemplate}</lion-collapsible> `;
 const collapsibleWithEvents = html`
-  <lion-collapsible @opened-changed=${e => collapsibleToggle(e.target.opened)}>
+  <lion-collapsible
+    @opened-changed=${/** @param {Event} e */ e =>
+      collapsibleToggle(/** @type {LionCollapsible} */ (e.target)?.opened)}
+  >
     ${collapsibleTemplate}
   </lion-collapsible>
 `;
@@ -47,7 +58,7 @@ describe('<lion-collapsible>', () => {
     it('opens a invoker on click', async () => {
       const collapsible = await fixture(defaultCollapsible);
       const invoker = collapsible.querySelector('[slot=invoker]');
-      invoker.dispatchEvent(new Event('click'));
+      invoker?.dispatchEvent(new Event('click'));
       expect(collapsible.opened).to.equal(true);
     });
 
@@ -93,7 +104,7 @@ describe('<lion-collapsible>', () => {
         const collapsibleElement = await fixture(defaultCollapsible);
         const invoker = collapsibleElement.querySelector('[slot=invoker]');
         const content = collapsibleElement.querySelector('[slot=content]');
-        expect(invoker.getAttribute('aria-controls')).to.equal(content.id);
+        expect(invoker?.getAttribute('aria-controls')).to.equal(content?.id);
       });
 
       it('adds aria-expanded="false" to invoker when its content is not expanded', async () => {
@@ -116,7 +127,7 @@ describe('<lion-collapsible>', () => {
         const collapsibleElement = await fixture(defaultCollapsible);
         const invoker = collapsibleElement.querySelector('[slot=invoker]');
         const content = collapsibleElement.querySelector('[slot=content]');
-        expect(content).to.have.attribute('aria-labelledby', invoker.id);
+        expect(content).to.have.attribute('aria-labelledby', invoker?.id);
       });
     });
   });
diff --git a/tsconfig.json b/tsconfig.json
index fb65d1d3e..f672325f4 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -18,6 +18,7 @@
     "packages/accordion/**/*.js",
     "packages/button/src/**/*.js",
     "packages/checkbox-group/**/*.js",
+    "packages/collapsible/**/*.js",
     "packages/core/**/*.js",
     "packages/fieldset/**/*.js",
     "packages/form/**/*.js",